Head-mounted display device

ABSTRACT

A HMD device including a display device, a first waveguide element and a second waveguide element is provided. An image beam is projected to a projection target. The first waveguide element includes a plurality of first light splitting elements. The image beam coming from the display device is incident to the first waveguide element through a first light incident surface. The image beam is convergent to a first stop in the first waveguide element. The image beam leaves the first waveguide element through the first light exiting surface. The first stop is located in the first waveguide element. The second waveguide element includes a plurality of second light splitting elements. The image beam coming from the first waveguide element is incident to the second waveguide element through the second light incident surface.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefits of China application Ser.No. 201710043567.0, filed on Jan. 19, 2017, and China application Ser.No. 201710343433.0, filed on May 16, 2017. The entirety of each of theabove-mentioned patent applications is hereby incorporated by referenceherein and made a part of specification.

BACKGROUND OF THE INVENTION Field of the Invention

The invention relates to a display system, and particularly relates tohead-mounted display (HMD).

Description of Related Art

Near eye display (NED) and head-mounted display (HMD) are the mostpromising killer products of the next generation. Related applicationsof the NED technique are presently divided into an augmented reality(AR) technique and a virtual reality (VR) technique. Regarding the ARtechnique, relevant developers are currently working on how to providethe best image quality under the premise of light and slim.

In an optical architecture of using the HMD to implement the AR, afteran image beam used for displaying is sent by a projection device, theimage beam enters an eye of a user through waveguide. An image comingfrom a light valve and an external environmental beam enters the eye ofthe user through the waveguide, so as to achieve the effect of AR. InHMD products, since a distance between the waveguide and an opticalengine mechanism is too close, the environmental beam is blocked fromentering the eye of the user, which spoils a sense of immersion, and theeffectiveness of AR is greatly reduced.

Regarding a demand on the HMD, the HMD is expected to be closer to adesign of general myopia glasses or sunglasses, so that how to move thehuge optical engine to the outside of a user's visual area to avoidblocking a line of sight of the user is one of the most important issuescurrently. Moreover, a magnitude of a field of view (FOV) provided bythe HMD and a volume of the HMD are also important factors thatinfluence a user experience.

The information disclosed in this Background section is only forenhancement of understanding of the background of the describedtechnology and therefore it may contain information that does not formthe prior art that is already known to a person of ordinary skill in theart. Further, the information disclosed in the

Background section does not mean that one or more problems to beresolved by one or more embodiments of the invention was acknowledged bya person of ordinary skill in the art.

SUMMARY OF THE INVENTION

The invention is directed to a head-mounted display (HMD) device, whichis adapted to provide a large field of view (FOV), good display qualityand good image quality, and has a small volume.

In order to achieve one or a portion of or all of the objects or otherobjects, an embodiment of the invention provides a head-mounted display(HMD) device. The HMD device includes a display device, a firstwaveguide element and a second waveguide element. The display device isused for providing an image beam. The image beam is projected to aprojection target. The first waveguide element includes a first lightincident surface, a first light exiting surface, and a plurality offirst light splitting elements. The image beam coming from the displaydevice is incident to the first waveguide element through the firstlight incident surface. The image beam is convergent to a first stop inthe first waveguide element. The image beam leaves the first waveguideelement through the first light exiting surface. The first stop islocated in the first waveguide element. The second waveguide elementincludes a second light incident surface, a second light exiting surfaceand a plurality of second light splitting elements. The image beamcoming from the first waveguide element is incident to the secondwaveguide element through the second light incident surface. The imagebeam leaves the second waveguide element through the second lightexiting surface.

In order to achieve one or a portion of or all of the objects or otherobjects, another embodiment of the invention provides a HMD device. TheHMD device includes a first waveguide element and a second waveguideelement. The first waveguide element includes a first light incidentsurface, a first light exiting surface, and a plurality of first lightsplitting elements. An image beam is incident to the first waveguideelement through the first light incident surface. The image beam isconvergent to a first stop in the first waveguide element, and the imagebeam leaves the first waveguide element through the first light exitingsurface. The first stop is located in the first waveguide element. Thesecond waveguide element includes a second light incident surface, asecond light exiting surface and a plurality of second light splittingelements. The image beam coming from the first waveguide element isincident to the second waveguide element through the second lightincident surface. The image beam leaves the second waveguide elementthrough the second light exiting surface.

Other objectives, features and advantages of the invention will befurther understood from the further technological features disclosed bythe embodiments of the invention wherein there are shown and describedpreferred embodiments of this invention, simply by way of illustrationof modes best suited to carry out the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1 is a three-dimensional view of a head-mounted display (HMD)device according to an embodiment of the invention.

FIG. 2A is a side view of the HMD of FIG. 1.

FIG. 2B is a side view of an optical path of the HMD device of theembodiment of FIG. 2A.

FIG. 2C is a side view of a HMD device according to another embodimentof the invention.

FIG. 3 is a three-dimensional view of a HMD device according to anotherembodiment of the invention.

FIG. 4 is a three-dimensional view of a HMD device according to anotherembodiment of the invention.

FIG. 5A is a schematic diagram of a HMD device according to anembodiment of the invention.

FIG. 5B is a schematic diagram of a HMD device according to anembodiment of the invention.

FIG. 5C is a schematic diagram of a HMD device according to anembodiment of the invention.

FIG. 6A is a schematic diagram of a HMD device according to anotherembodiment of the invention.

FIG. 6B is a schematic diagram of a HMD device according to anotherembodiment of the invention.

FIG. 7 is a top view of a second waveguide element of FIG. 1.

FIG. 8 is a schematic diagram of reflectivity distribution curves ofreflectivities of a diffusion coating film relative to incident anglesof an image beam according to an embodiment of the invention.

FIG. 9 is a schematic diagram of an image frame produced at a projectiontarget by an image beam of the embodiment of FIG. 7.

FIG. 10 is a side view of a first waveguide element of FIG. 1.

FIG. 11 is a schematic diagram of an image frame produced at aprojection target by an image beam of the embodiment of FIG. 10.

FIG. 12A is a schematic diagram of superposing image frames produced atthe projection target by the image beam of the embodiments of FIG. 9 andFIG. 11.

FIG. 12B is a schematic diagram of reflecting image beams to theprojection target by different second light splitting elements.

FIG. 13 is a schematic diagram of an image beam incident to a secondwaveguide element from first light splitting elements according to anembodiment of the invention.

FIG. 14A is a schematic diagram of an image beam incident to a firstlight splitting element according to an embodiment of the invention.

FIG. 14B is a schematic diagram of an image beam incident to the firstlight splitting element according to an embodiment of the invention.

FIG. 15 is a schematic diagram of a HMD device according to anembodiment of the invention.

FIG. 16 is a schematic diagram of a HMD device according to anembodiment of the invention.

FIG. 17 is a schematic diagram of a HMD device according to anembodiment of the invention.

FIG. 18 is a schematic diagram of a part of elements of the HMD deviceof the embodiment of FIG. 17.

FIG. 19 is a schematic diagram of a HMD device according to anembodiment of the invention.

FIG. 20 is a schematic diagram of a HMD device according to anembodiment of the invention.

FIG. 21 is a schematic diagram of a HMD device according to anembodiment of the invention.

DESCRIPTION OF EMBODIMENTS

In the following detailed description of the preferred embodiments,reference is made to the accompanying drawings which form a part hereof,and in which are shown by way of illustration specific embodiments inwhich the invention may be practiced. In this regard, directionalterminology, such as “top,” “bottom,” “front,” “back,” etc., is usedwith reference to the orientation of the Figure(s) being described. Thecomponents of the invention can be positioned in a number of differentorientations. As such, the directional terminology is used for purposesof illustration and is in no way limiting. On the other hand, thedrawings are only schematic and the sizes of components may beexaggerated for clarity. It is to be understood that other embodimentsmay be utilized and structural changes may be made without departingfrom the scope of the invention. Also, it is to be understood that thephraseology and terminology used herein are for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having” and variations thereof herein ismeant to encompass the items listed thereafter and equivalents thereofas well as additional items. Unless limited otherwise, the terms“connected,” “coupled,” and “mounted” and variations thereof herein areused broadly and encompass direct and indirect connections, couplings,and mountings. Similarly, the terms “facing,” “faces” and variationsthereof herein are used broadly and encompass direct and indirectfacing, and “adjacent to” and variations thereof herein are used broadlyand encompass directly and indirectly “adjacent to”. Therefore, thedescription of “A” component facing “B” component herein may contain thesituations that “A” component directly faces “B” component or one ormore additional components are between “A” component and “B” component.Also, the description of “A” component “adjacent to” “B” componentherein may contain the situations that “A” component is directly“adjacent to” “B” component or one or more additional components arebetween “A” component and “B” component. Accordingly, the drawings anddescriptions will be regarded as illustrative in nature and not asrestrictive.

FIG. 1 is a three-dimensional view of a head-mounted display (HMD)device according to an embodiment of the invention. FIG. 2A is a sideview of the HMD of FIG. 1. Referring to FIG. 1 and FIG. 2A, the HMD 100of the embodiment includes a first waveguide element 110, a secondwaveguide element 120, a display device 130 and a lens module 140. Thesecond waveguide element 120 is connected to the first waveguide element110. The lens module 140 is disposed between the display device 130 andthe first waveguide element 110.

In the embodiment, the first waveguide element 110 includes a firstlight incident surface S11, a first light exiting surface S12, and aplurality of first light splitting elements Y1, Y2, Y3, Y4. The firstlight splitting elements Y1, Y2, Y3, Y4 are arranged along a firstdirection Y. In the embodiment, the first light incident surface S11 isdisposed opposite to the first light exiting surface S12, though theinvention is not limited thereto. In an embodiment, based on differentconfiguration positions of the display device 130, the first lightincident surface S11 may also be connected to the first light exitingsurface S12. In the embodiment, an image beam ML has a trans-reflectiveoptical effect at positions of the first light splitting elements Y1,Y2, Y3, Y4, and the first light splitting elements Y1, Y2, Y3, Y4 are,for example, see through mirrors (STM). In the embodiment, the secondwaveguide element 120 includes a second light incident surface S21, asecond light exiting surface S22 and a plurality of second lightsplitting elements X1, X2, X3, X4, X5, X6, where the second lightincident surface S21 and the second light exiting surface S22 belong toa same surface, and the second light incident surface S21 of the secondwaveguide element 120 faces the first light exiting surface S12 of thefirst waveguide element 110. The second light splitting elements X1, X2,X3, X4, X5, X6 are arranged along a second direction X. In theembodiment, the image beam ML has the trans-reflective optical effect atpositions of the second light splitting elements X1, X2, X3, X4, X5, X6.In the embodiment, the number of the light splitting elements includedin each of the waveguide elements and a gap between adjacent lightsplitting elements may be designed according to different productrequirements, and are not limited by the invention. Moreover, the numberof the first light splitting elements may be the same or different tothe number of the second light splitting elements, and the gaps betweenthe adjacent light splitting elements may be the same or different. Inthe embodiment, the display device 130 is used for converting anillumination beam coming from an illumination system into the image beamML, so as to provide the image beam ML to the lens module 140, where theillumination system is described in detail below. In the embodiment, thedisplay device 130, for example, includes digital micromirror devices(DMD) in a digital light processing™ (DLP™) projection system, aliquid-crystal display (LCD) projection system or a liquid crystal onsilicon (LCoS) projection system, etc., which is not limited by theinvention. In the embodiment, the lens module 140 is, for example, oneor a plurality of lenses, and the quantity thereof is not limited and isdetermined according to an actual design requirement. The lens module140 has an optical axis A1 extending along a third direction Z. Theimage beam ML is transmitted along the third direction Z in the lensmodule 140. The image beam ML coming from the display device 130 passesthrough the lens module 140, and is incident to the first waveguideelement 110 through the first light incident surface S11. In theembodiment, the image beam ML in the first waveguide element 110 passesthrough the first light splitting element Y1 and is transmitted alongthe first direction Y, and after the reflection function of the firstlight splitting elements Y1, Y2, Y3, Y4, the image beam ML leaves thefirst waveguide element 110 through the first light exiting surface S12along an opposite direction (−Z) of the third direction Z. It should benoted that the first light splitting elements Y1, Y2, Y3, Y4 are seethrough mirrors, i.e. a part of the image beam ML is reflected by thefirst light splitting elements Y1, Y2, Y3, Y4, and a part of the imagebeam ML penetrates through the first light splitting elements Y1, Y2,Y3, Y4. In the embodiment, an optical path of the image beam ML is adescription focus.

Moreover, the image beam ML coming from the first waveguide element 110is incident to the second waveguide element 120 through the second lightincident surface S21 along the opposite direction (−Z) of the thirddirection Z, and is transmitted to the second light splitting elementsX1, X2, X3, X4, X5, X6 of the second waveguide element 120 after beingreflected by a reflection surface S23 of the second waveguide element120. In the embodiment, the image beam ML in the second waveguideelement 120 is transmitted along the second direction X, and after thereflection function of the second light splitting elements X1, X2, X3,X4, X5, X6, the image beam ML leaves the second waveguide element 120through the second light exiting surface S22 and is projected to aprojection target P. Therefore, in the embodiment, the second lightincident surface S21 and the second light exiting surface S22 are a samesurface of the second waveguide element 120, though the second lightexiting surface S22 faces the projection target P. In the embodiment,the projection target P is, for example, a pupil, which is one of theeyes of the user. In other embodiment, the projection target P is, forexample, an image sensing device used for receiving the image beam ML,for example, a charge-coupled device (CCD), or a complementarymetal-oxide-semiconductor image sensor (CMOS image sensor).

In the embodiment, the image beam ML is transmitted in the lens module140 along the opposite direction (−Z) of the third direction Z, where atransmitting direction thereof is substantially the same to an extendingdirection of the optical axis A1. In the embodiment, the projectiontarget P has a visual axis A2, where an extending direction thereof (thethird direction Z) is substantially the same to the transmittingdirection of the image beam ML projected to the projection target P, andis perpendicular to the first direction Y. Therefore, in FIG. 1, bytranslating the visual axis A2 of the projection target P to a YZ plane(a reference plane) in the first waveguide element 110, a reference axisA3 is indicated in the first waveguide element 110, as shown in FIG. 2A.

Namely, in the embodiment, the projection target P has the visual axisA2 perpendicular to the first direction Y, and the visual axis A2 istranslated to the reference axis A3 on the reference plane YZ in thefirst waveguide element 110. In FIG. 2A, on the reference plane YZ, andon a transmission path of the illumination beam ML, a distance between afirst stop PA1 formed by the illumination beam ML and a center positionPC of the first light splitting element Y1 of the first light splittingelements Y1, Y2, Y3, Y4 in the first direction Y is D1, and a distancebetween the reference axis A3 and the center position PC of the firstlight splitting element Y1 in the first direction Y is D2. In theembodiment, the distance D1 is greater than or equal to the distance D2.The first light splitting element Y1 is one of the first light splittingelements that first reflects the image beam ML after a part of the imagebeam ML enters the first waveguide element 110, and is one of the firstlight splitting elements Y1, Y2, Y3, Y4 that is located the closest tothe lens module 140.

In the embodiment, the image beam ML coming from the lens module 140 isconvergent to the first stop PA1 in the first waveguide element 110. Thefirst stop PA1 is located in the first waveguide element 110. In theembodiment, the first stop PA is a position where the image beam ML isconvergent to the minimum beam diameter within the first waveguideelement 110, and after the image beam ML passes through the position ofthe first stop PA, the image beam ML starts to be divergent. Forexample, the lens module 140 makes the image beam ML incident to thefirst waveguide element 110 to start converging from the first lightsplitting element Y1, and reach the minimum beam diameter at the firststop PAL After passing through the first stop PA1, the image beam MLstarts to be divergent and is incident to the first light splittingelement Y4 and is reflected to the first light exiting surface S12. Inthe embodiment, after the image beam ML leaves the second waveguideelement 120 through the second light exiting surface S22, the image beamML is projected to a second stop PA2 outside the second waveguideelement 120. The second stop PA2 is located at the projection target P.For example, the second light splitting elements X1, X2, X3, X4, X5, X6may reflect the image beam ML incident to the second waveguide element120 to leave the second waveguide element 120 through the second lightexiting surface S22, and the image beam ML is projected to the positionof the second stop PA2, such that the image beam ML may be incident tothe projection target P, where the position of the second stop PA2 issubstantially the same to the position of the projection target P, i.e.a position where one of the eyes of the user may view the image, i.e.the position of the second stop PA2.

In the embodiment, a field of view (FOV) of the lens module 140corresponds to a FOV of an image received at the projection target P. Inother words, in the embodiment, a diagonal FOV of the image formed bythe image beam ML received at the projection target P is substantiallyequal to a FOV of the image beam ML projected by the lens module 140. Inother embodiments, the diagonal FOV of the image formed by the imagebeam ML received at the projection target P is substantially smallerthan the FOV of the image beam ML projected by the lens module 140.

Based on the diagonal FOV of the image formed by the image beam ML, afirst FOV in the first direction Y and a second FOV in the seconddirection X are learned. In the embodiment, when the display device 130projects the image beam ML to display an image with a projection ratioof 16:9, the image beam ML with the diagonal FOV of about 30 degrees to90 degrees, for example, 40 degrees is projected through the lens module140 to pass through the first waveguide element 110 and the secondwaveguide element 120, and is transmitted to the projection target P,such that the diagonal FOV of the image formed by the image beam MLreceived at the projection target P is about 30 degrees to 90 degrees,for example, 40 degrees, though the invention is not limited thereto.Those skilled in the art may calculate that the first FOV in the firstdirection Y is 10 degrees and the second FOV in the second direction Xis about 17 degrees according to the projection ratio of 16:9.Therefore, by using the HMD device of the invention, the diagonal FOV ofthe image formed by the image beam ML received at the projection targetP is about 30-90 degrees or above 90 degrees. Moreover, as shown in FIG.2A, in another embodiment, the optical axis A1 of the lens module 140 isperpendicular to the first direction Y and is parallel to the visualaxis A2 of the projection target P, and the diagonal FOV of the imageformed by the image beam ML received at the projection target P may be30-50 degrees. As shown in FIG. 3, in another embodiment, the opticalaxis A1 of the lens module 140 is parallel to the first direction Y andis perpendicular to the visual axis A2 of the projection target P, andthe diagonal FOV of the image formed by the image beam ML received atthe projection target P may be 50-90 degrees. The diagonal FOV may bedesigned according to different product requirements, which is notlimited by the invention. The HMD device 100 may provide a large FOV andhas a small volume.

In other embodiments, after the image beam ML projected by the lensmodule 140 forms the diagonal FOV, a magnitude of the first FOV may bedetermined according to the number of the first light splitting elementsin the first waveguide element 110, or determined according to adistance between the first piece of the first light splitting elementsand the last piece of the first light splitting elements in the firstwaveguide element 110, or determined according to a distance between twoadjacent first light splitting elements in the first waveguide element110. Similarly, a magnitude of the second FOV is, for example,determined according to the number of the second light splittingelements in the second waveguide element 120, or determined according toa distance between the first piece of the second light splittingelements and the last piece of the second light splitting elements inthe second waveguide element 120, or determined according to a distancebetween two adjacent second light splitting elements in the secondwaveguide element 120. It should be noted that the magnitude of thefirst FOV and the magnitude of the second FOV generated through theadjustment of the first waveguide element 110 and the second waveguideelement 120 may all be smaller than or equal to the magnitude of thefirst FOV and the magnitude of the second FOV of the image formed by theimage beam ML projected by the lens module 140.

Moreover, considering the image projection ratio provided by the displaydevice 130 may influence the number of the first light splittingelements of the first waveguide element 110 and the number of the secondlight splitting elements of the second waveguide element 120, forexample, if the projection ratio is 16:9, the number of the second lightsplitting elements of the second waveguide element 120 is greater thanthe number of the first light splitting elements of the first waveguideelement 110. However, in other design conditions, the number of thesecond light splitting elements of the second waveguide element 120 maybe smaller than the number of the first light splitting elements of thefirst waveguide element 110, which is not limited by the invention.

Moreover, based on different configuration positions of the displaydevice and the lens module, in an embodiment, the first light incidentsurface of the first waveguide element may be adjacent to the firstlight exiting surface, and the optical axis of the lens module isparallel to the first direction. In an embodiment, the first lightincident surface of the first waveguide element may be adjacent to thefirst light exiting surface, and the optical axis of the lens module maybe perpendicular to the first direction and parallel to the seconddirection.

FIG. 2B is a side view of an optical path of the HMD device of theembodiment of FIG. 2A. Referring to FIG. 2B, since the first lightsplitting elements Y1, Y2, Y3, Y4 of the first waveguide element 110 areSTMs, i.e. a part of the image beam ML is reflected by the first lightsplitting elements Y1, Y2, Y3, Y4, and a part of the image beam MLpenetrates through the first light splitting elements Y1, Y2, Y3, Y4. Inthe embodiment, a part of the image beam ML in the first waveguideelement 110 is convergent to the position of the first stop PA1. Basedon a basic optical principle, it is known that a part of the image beamML that penetrates through the first light splitting element Y1 may alsobe convergent to a position of a stop PA1′ in the second waveguideelement 120, and a distance between a center position of the first lightsplitting element Y1 and the position of the stop PA1′ is equal to adistance between the center position of the first light splittingelement Y1 and the position of the first stop PA1. Similarly, a part ofthe image beam ML reflected by the first light splitting elements Y2 andY3 may also be convergent to positions of stops PA1″ and PA1″′ in thesecond waveguide element 120, and a distance between a center positionof the first light splitting element Y2 and the position of the stopPA1″ is equal to a distance between the center position of the firstlight splitting element Y2 and the position of the first stop PA1, and adistance between a center position of the first light splitting elementY3 and the position of the stop PA1″′ is equal to a distance between thecenter position of the first light splitting element Y3 and the positionof the first stop PAL

FIG. 2C is a side view of a HMD device according to another embodimentof the invention. The HMD device of the embodiment of FIG. 2C is asimilar to the HMD device 100 of the embodiment of FIG. 2A, andcomponents and related descriptions thereof may refer to the componentsand related descriptions of the HMD device 100, and details thereof arenot repeated. Differences of the two HMD devices 100 are described asfollows. In the embodiment, the HMD device 100 includes the firstwaveguide element 110 and the second waveguide element 120. Moreover,the HMD device 100 further includes a reflection mirror 150 disposedbeside the first light incident surface S11, and faces the first lightincident surface S11. The reflection mirror 150 is used for reflectingthe image beam ML provided by the display device 130 through the lensmodule 140, such that the image beam ML enters the first waveguideelement 110 from the first light incident surface S11. Then, the imagebeam ML entering the first waveguide element 110 may be reflected by aplurality of the first light splitting elements Y1, Y2, Y3, Y4 andtransmitted to the second waveguide element 120.

To be specific, an included angle between the reflection mirror 150 andthe first light incident surface S11 is, for example, 45 degrees. Afterthe image beam ML is reflected by the reflection mirror 150, the imagebeam ML is incident to the first light splitting element Y1. Moreover,in the embodiment, the position of the first stop PA1 of the image beamML is, for example, located in the first waveguide element 110. Theposition of the first stop PA1 is located amount the first lightsplitting elements Y1, Y2, Y3, Y4. Therefore, the image beam MLtransmitted in the first waveguide element 110 may be converged to theposition of the first stop PA1. In the embodiment, by setting theposition of the first stop PA1 whereto the image beam ML is converged inthe internal of the first waveguide element 110, a situation that theimage beam ML is too early to diverge on the XY plane to cause a totalreflection at the first light exiting surface S12 and the first lightincident surface S11 is avoided. Namely, the image beam ML may be guidedto the second waveguide element 120 through the first light splittingelements Y1, Y2, Y3, Y4 before the total reflection is occurred, so thatthe image beam ML is avoided to have the total reflection in the firstwaveguide element 110 to cause the problem of unexpected display image.

FIG. 3 is a three-dimensional view of a HMD device according to anotherembodiment of the invention. Referring to FIG. 1 and FIG. 3, the HMDdevice 200 of the embodiment is similar to the HMD device 100 of theembodiment of FIG. 1, and a difference therebetween is that a displaydevice 230 and a lens module 240 of the HMD device 200 are disposed inparallel at a side edge of the first waveguide element 210, and theimage beam ML coming from the lens module 240 is incident to the firstwaveguide element 210 from the first light incident surface S13 of thefirst waveguide element 210, and leaves the first waveguide element 210through the first light exiting surface S12. Therefore, in theembodiment, the first light incident surface S13 of the first waveguideelement 210 is contiguous to the first light exiting surface S12, andthe optical axis A1 of the lens module 240 is parallel to the firstdirection Y. In the embodiment, the first stop PA1 is located in thefirst waveguide element 210, and the second stop PA2 is located at theprojection target P. Moreover, a position of the first stop PA1 in thefirst waveguide element 210 is complied with a condition that thedistance D1 is greater than or equal to the distance D2.

FIG. 4 is a three-dimensional view of a HMD device according to anotherembodiment of the invention. Referring to FIG. 1 and FIG. 3, the HMDdevice 800 of the embodiment is similar to the HMD device 100 of theembodiment of FIG. 1, and a difference therebetween is that the firstlight incident surface is contiguous to the first light exiting surface,and the optical axis A1 of the lens module is perpendicular to the firstdirection Y and parallel to the second direction X.

To be specific, in the embodiment, the HMD device 800 includes a firstwaveguide element 810, a second waveguide element 820, a third waveguideelement 850, a display device 830 and a lens module 840. In anembodiment the third waveguide element 850 and the second waveguideelement 820 are made of a same material and are structures formedintegrally. The display device 830 is used for providing the image beamML. In the embodiment, the image beam ML is incident to the firstwaveguide element 810 through the first light incident surface S14, andis reflected by a reflecting surface S15 to transmit towards the firstdirection Y. Then, the image beam ML leaves the first waveguide element810 through the first light exiting surface S12. Therefore, in theembodiment, the first light incident surface S14 is contiguous to thefirst light exiting surface S12 and the reflecting surface S15, and theoptical axis A1 of the lens module 840 is perpendicular to the firstdirection Y and parallel to the second direction X. Configurationpositions of the display device 830 and the lens module 840 may bedetermined according to different product designs or opticalcharacteristics, which are not limited by the invention. Moreover, thethird waveguide element 850 of the embodiment may adopt a device designof a third waveguide element of one of the embodiments of FIG. 5A-FIG.5C.

In the embodiment, the first waveguide element 810 includes a pluralityof first light splitting elements 811. The image beam ML has thetrans-reflective optical effect at the positions of the first lightsplitting elements 811, and is incident to the third waveguide element850. The third waveguide element 850 may have a reflecting structureshown in the embodiments of FIG. 5A-FIG. 5C. In the embodiment, theimage beam ML is reflected at a position of the reflecting structure ofthe third waveguide element 850, and is incident to the second waveguideelement 820. The second waveguide element 820 includes a plurality ofsecond light splitting elements 831. The image beam ML has thetrans-reflective optical effect at the positions of the second lightsplitting elements 831, and leaves the second waveguide element 820. Inthe embodiment, the image beam ML leaving the second waveguide element820 enters the projection target P, where the projection target P is,for example, at a position of an eye of the user. Moreover, the numbersof the first light splitting elements 811 and the second light splittingelements 831 are not limited to the number shown in FIG. 4, and thenumber of the light splitting elements configured in the first waveguideelement 810 and the second waveguide element 820 may be designedaccording to different product requirements, and is not limited by theinvention.

In the embodiment, since the first light splitting elements 811 and thesecond light splitting elements 831 respectively have coating films, andthe coating films are only pervious to the image beam ML incident withina specific incident angle range, when the image beam ML is incident tothe first light splitting elements 811 and the second light splittingelements 831 in an excessive large angle during the process of beingtransmitted in the first waveguide element 810 and the second waveguideelement 820, a part of the image beam ML is reflected by the first lightsplitting elements 811 and the second light splitting elements 831. Theunexpected reflected image beam ML is continually transmitted in thefirst waveguide element 810 and the second waveguide element 820, and incase that the image beam ML is subsequently incident to the lightsplitting elements in a smaller angle, the image beam ML is obliquelyguided to the eye of the user in a direction opposite to theaforementioned expected direction. Now, besides that the user may viewan original expected image frame, the user may also view a mirroredunexpected image frame. Therefore, the user is easy to feel a ghostphenomenon of the image frame or the image frame is blurred during theprocess of using the HMD device.

FIG. 5A is a schematic diagram of a HMD device according to anembodiment of the invention. Referring to FIG. 5A, in the embodiment,the HMD device 500 includes a first waveguide element 510, a secondwaveguide element 520 and a third waveguide element 530, where thesecond waveguide element 520 includes a plurality of second a pluralityof second light splitting elements 531. In the embodiment, the firstwaveguide element 510 is disposed beside the third waveguide element530. The first waveguide element 510 may be attached to the thirdwaveguide element 530, or the first waveguide element 510 and the thirdwaveguide element 530 may be adhered through a transparent adhesivematerial, or fixing members 532 (for example, spacers or adhesivematerials or pads) may be disposed at the periphery of the firstwaveguide element 510 and the third waveguide element 530 to form a gaptherebetween, where the gap may be a tiny air gap. Moreover, a firstlight exiting surface ES1 faces a second light incident surface IS2. Thesecond light incident surface IS2 is connected to a second light exitingsurface ES2. The third waveguide element 530 may be attached to thesecond waveguide element 520, or the third waveguide element 530 and thesecond waveguide element 520 may be adhered through the transparentadhesive material. Therefore, a third light incident surface IS3 isconnected to the second light exiting surface ES2. In the embodiment,the third waveguide element 530 includes a reflecting structure 521. Thereflecting structure 521 may be composed of a plurality of opticalmicrostructures, and the optical microstructures may be a plurality ofreflecting surfaces periodically arranged in a tilt configuration.

Moreover, a purpose of the aforementioned air gap is that when the imagebeam ML with a large incident angle is incident to the first waveguideelement 510, a situation that a part of the image beam ML directlypenetrates through the first waveguide element 510 is avoided, such thatthe part of the image beam ML is transmitted in the first waveguideelement 510 in a total reflection manner. Another purpose of the air gapis that a part of the image beam ML is reflected towards the secondlight incident surface IS2 by the reflecting structure 521, and due tothe air gap, a part of the image beam ML has the total reflection at thesecond light incident surface IS2, and the part of the image beam ML isguided to the second waveguide element 520.

In the embodiment, the image beam ML is incident to the third waveguideelement 530 through the first light exiting surface ES1 of the firstwaveguide element 510, and is incident to the third waveguide element530 through the second light incident surface IS2. The image beam MLcoming from the second light incident surface IS2 is reflected by thereflecting structure 521, and leaves the third waveguide element 530through the second light exiting surface ES2. The image beam ML isincident to the second waveguide element 520 through the third lightincident surface IS3, and leaves the second waveguide element 520through a third light exiting surface ES3.

In the embodiment, materials of the third waveguide element 530 and thesecond waveguide element 520 may be different. For example, the materialof the third waveguide element 530 may be a plastic material, and thematerial of the first waveguide element 510 and the second waveguideelement 520 may be glass, though the invention is not limited thereto.In an embodiment, the third waveguide element 530 and the secondwaveguide element 520 may have the same material and may be a structureformed integrally. In the embodiment, the respective materials of thefirst waveguide element 510, the third waveguide element 530 and thesecond waveguide element 520 may be determined according to differentreflection requirements or product designs.

FIG. 5B is a schematic diagram of a HMD device according to anembodiment of the invention. Referring to FIG. 5B, in the embodiment,the HMD device 600 includes a first waveguide element 610, a thirdwaveguide element 630 and a second waveguide element 620, where thesecond waveguide element 620 includes a plurality of second a pluralityof second light splitting elements 631. In the embodiment, the firstwaveguide element 610 is disposed beside the second waveguide element620. The first waveguide element 610 may be attached to the secondwaveguide element 620, or the first waveguide element 610 and the secondwaveguide element 620 may be adhered through a transparent adhesivematerial, or mechanism members (for example, spacers or adhesivematerials) may be disposed at the periphery of the first waveguideelement 610 and the second waveguide element 620 to form a gaptherebetween, where the gap may be a tiny air gap. Therefore, on atransmission path of the image beam ML, the image beam ML penetratesthrough the second waveguide element 620 through the first light exitingsurface ES1, and is transmitted to the third waveguide element 630.Moreover, the first light exiting surface ES1 faces the second lightincident surface IS2. The second light incident surface IS2 is connectedto the second light exiting surface ES2. The third waveguide element 630may be attached to the second waveguide element 620, or the thirdwaveguide element 630 and the second waveguide element 620 may beadhered through the transparent adhesive material. Therefore, the thirdlight incident surface IS3 is connected to the second light exitingsurface ES2. The second light incident surface IS2 and the third lightincident surface IS3 face the first light exiting surface ES1. In theembodiment, the third waveguide element 630 includes a reflectingstructure 621. The reflecting structure 621 may be composed of aplurality of optical microstructures, and the optical microstructuresmay be a plurality of reflecting surfaces periodically arranged in atilt configuration.

In the embodiment, the image beam ML is incident to the second waveguideelement 620 through the first light exiting surface ES1 of the firstwaveguide element 610, and is incident to the third waveguide element630 through the second light incident surface IS2 after passing throughthe second waveguide element 620. The image beam ML coming from thesecond light incident surface IS2 is reflected by the reflectingstructure 621, and leaves the third waveguide element 630 through thesecond light exiting surface ES2. The image beam ML is incident to thesecond waveguide element 620 through the third light incident surfaceIS3, and leaves the second waveguide element 620 through the third lightexiting surface ES3.

In the embodiment, materials of the third waveguide element 630 and thesecond waveguide element 620 may be different. For example, the materialof the third waveguide element 630 may be a plastic material, and thematerial of the first waveguide element 610 and the second waveguideelement 620 may be glass, though the invention is not limited thereto.In an embodiment, the third waveguide element 630 and the secondwaveguide element 620 may have the same material and may be a structureformed integrally. In the embodiment, the respective materials of thefirst waveguide element 610, the third waveguide element 630 and thesecond waveguide element 620 may be determined according to differentreflection requirements or product designs.

FIG. 5C is a schematic diagram of a HMD device according to anembodiment of the invention. Referring to FIG. 5C, in the embodiment,the HMD device 700 includes a first waveguide element 710, a thirdwaveguide element 730 and a second waveguide element 720, where thesecond waveguide element 720 includes a plurality of second a pluralityof second light splitting elements 731. In the embodiment, the firstwaveguide element 710 is disposed beside the second waveguide element720. The first waveguide element 710 may be attached to the secondwaveguide element 720, or the first waveguide element 710 and the secondwaveguide element 720 may be adhered through a transparent adhesivematerial, or fixing members (for example, spacers or adhesive materialsshown in FIG. 5A) may be disposed at the periphery of the firstwaveguide element 710 and the second waveguide element 720 to form a gaptherebetween, where the gap may be a tiny air gap. Therefore, the firstlight exiting surface ES1 faces the second light incident surface IS2through the second waveguide element 720. The second light incidentsurface IS2 is connected to the second light exiting surface ES2. Thethird waveguide element 730 is obliquely disposed beside the secondwaveguide element 720, so that the second light incident surface IS2,the second light exiting surface ES2 and the third light incidentsurface IS3 have a tilt angle relative to the third light exitingsurface ES3. The third waveguide element 730 may be attached to thesecond waveguide element 720, or the third waveguide element 730 and thesecond waveguide element 720 are adhered through the transparentadhesive material. Therefore, the third light incident surface IS3 isconnected to the second light exiting surface ES2. In the embodiment,the third waveguide element 730 includes a reflecting structure 721 anda transparent layer. The third waveguide element 730 is a reflectingunit, and the reflecting structure 721 may be a reflecting mirror or areflective coating layer.

In the embodiment, the image beam ML is incident to the second waveguideelement 720 through the first light exiting surface ES1 of the firstwaveguide element 710, and is incident to the third waveguide element730 through the second light incident surface IS2 after passing throughthe second waveguide element 720. The image beam ML coming from thesecond light incident surface IS2 is reflected by the reflectingstructure 721, and leaves the third waveguide element 730 through thesecond light exiting surface ES2. The image beam ML is incident to thesecond waveguide element 720 through the third light incident surfaceIS3, and leaves the second waveguide element 720 through the third lightexiting surface ES3.

In the embodiment, materials of the first waveguide element 710, thethird waveguide element 730 and the second waveguide element 720 may allbe a glass material, though the invention is not limited thereto. In anembodiment, the third waveguide element 730 may be a reflecting unitmade of a plastic material. Moreover, the respective materials of thefirst waveguide element 710, the third waveguide element 730 and thesecond waveguide element 720 may be determined according to differentreflection requirements or product designs.

FIG. 6A is a schematic diagram of a HMD device according to anotherembodiment of the invention. Referring to FIGS. 1-4 and FIG. 6A, in theembodiment, the HMD device 900 includes a first waveguide element 910, athird waveguide element 930, a second waveguide element 920 and areflecting element 950. The reflecting element 950 is used for receivingthe image beam ML provided by the display device, and the reflectingelement 950 may be a prism (not shown) having a reflecting layer, andthe image beam ML provided by the display device is incident to thereflecting element 950 along the X-axis direction, and the reflectinglayer of the reflecting element 950 reflects the image beam ML to enterthe first waveguide element 910 along the Y-axis direction. Forconvenience of description, the third waveguide element 930 of theembodiment adopts the design of the reflecting structure of the secondwaveguide element of the embodiment of FIG. 5C, though the invention isnot limited thereto. The design of the reflecting structure of thesecond waveguide element of the embodiments of FIG. 5A and FIG. 5B mayalso be adopted.

In the embodiment, the image beam ML provided by the display device ofthe invention may only have a single polarized direction. For example,when the image beam ML is reflected by the reflecting element 950 toenter the first waveguide element 910, a polarizer 960 may be appliedbetween the display device and the first waveguide element 910, betweenthe display device and the reflecting element 950, or between thereflecting element 950 and the first waveguide element 910, such thatthe image beam ML incident to the first waveguide element 910 from thedisplay device is only the light having a P-polarized direction (thedirection of the third axis Z), and the image beam ML is incident to thesecond waveguide element 920 from the first waveguide element 910through the reflecting structure of the third waveguide element 930, andbased on an optical definition of the basic polarized light of thisfield, it is known that the light with the P-polarized direction isconverted into the light with an S-polarize direction (the direction ofthe second axis X). Therefore, in the first waveguide element 910, onlythe image beam with the single polarized direction is transmitted, andthe respectively coating films of the first light splitting elements 911and the second light splitting elements 931 may designed correspondingto the image beam having the single polarized direction.

In another embodiment, the HMD device 900 of the embodiment may furtherinclude a phase delay sheet 970. In the embodiment, the polarizer 960may be disposed between the display device and the first waveguideelement 910, or between the reflecting element 950 and the firstwaveguide element 910, such that the image beam incident to the firstwaveguide element 910 from the reflecting element 950 may only have thelight with the S-polarized direction. Moreover, the phase delay sheet970 may be disposed between the first waveguide element 910 and thethird waveguide element 930 (and the phase delay sheet 970 may also bedisposed between the second waveguide element 920 and the firstwaveguide element 910), such that the image beam incident to the secondwaveguide element 920 from the first waveguide element 910 may be thelight with the S-polarized direction. Therefore, in the HMD device 900,by configuring the polarizer 960 and the phase delay sheet 970,transmission of the unexpected reflected light in the first waveguideelement 910 and the second waveguide element 920 is effectivelymitigated.

FIG. 6B is a schematic diagram of a HMD device 900A according to anotherembodiment of the invention. The image beam ML provided by the displaydevice 830 may only have the single polarized direction. For example,the image beam ML directly incident to the first waveguide element 910may have the light with the P-polarized direction (the direction of thethird axis Z), and the image beam ML is incident to the second waveguideelement 920 from the first waveguide element 910 through the reflectingstructure, and is naturally converted into the image beam ML with theS-polarized direction (the direction of the first axis Y) based on abasic optical reflection effect. Therefore, only the image beam ML withthe single polarized direction is transmitted in the first waveguideelement 910, and the respective coating films of the first lightsplitting elements 911 and the second light splitting elements 931 maybe designed corresponding to the image beam ML having the singlepolarized direction. Therefore, in the HMD device 900A of theembodiment, transmission of the unexpected reflected light in the firstwaveguide element 910 and the second waveguide element 920 iseffectively mitigated. In the embodiment, the first stop PA1 is alsolocated in the first waveguide element 910, and the second stop PA2 islocated at the projection target P. Moreover, a position of the firststop PA1 in the first waveguide element 910 is complied with a conditionthat the distance D1 is greater than or equal to the distance D2.

FIG. 7 is a top view of the second waveguide element of FIG. 1. FIG. 8is a schematic diagram of reflectivity distribution curves ofreflectivities of a diffusion coating film relative to incident anglesof the image beam according to an embodiment of the invention. In FIG.8, the reflectivity distribution curves of the reflectivities of thediffusion coating film relative to the incident angles of the imagebeam, for example, take a wavelength of 520 nm as an example fordescription, though the invention is not limited thereto. Moreover, thereflectivity distribution curves of FIG. 8 are only used as an example,and are not used for limiting the invention. Referring to FIG. 7 to FIG.8, in the embodiment, each of the second light splitting elements X1,X2, X3, X4, X5, X6 in the second waveguide element 120 includes a firstsurface and a second surface opposite to the first surface, and one ofthe first surface and the second surface may include the diffusioncoating film, for example, the first surface includes the diffusioncoating film. Taking the second light splitting element X1 as anexample, the second surface SX12 is opposite to the first surface SX11,and the first surface SX11 includes the diffusion coating film. In theembodiment, the image beam ML is incident to each of the second lightsplitting elements from the first surface of each of the second lightsplitting elements, and an incident angle of the image beam ML incidentto each of the second light splitting elements ranges between 15 degreesand 45 degrees, such that a part of the image beam ML is reflected to apupil P by the diffusion coating film, where an included angle betweeneach of the second light splitting elements in the second waveguideelement 120 and the second light exiting surface S22 is 30 degree,though the invention is not limited thereto. In the second waveguideelement 120, the polarized direction of the image beam ML is a secondpolarized direction (for example, an S-direction polarized light). Inthe embodiment, the reflectivity of the diffusion coating film is, forexample, complied with the reflectivity distribution curve of FIG. 8.When the incident angle is between 15 degrees and 45 degrees, thereflectivity of an Nth second light splitting element is smaller than orequal to the reflectivity of an (N+1)^(th) second light splittingelement, where N is an integer greater than or equal to 1. In FIG. 8, acurve SR(N+1) is, for example, the reflectivity distribution curve ofthe (N+1)^(th) second light splitting element, and a curve SRN is, forexample, the reflectivity distribution curve of the N^(th) second lightsplitting element. For example, the reflectivity of the 1^(st) secondlight splitting element X1 is smaller than or equal to the reflectivityof the 2^(nd) second light splitting element X2, though the invention isnot limited thereto.

FIG. 9 is a schematic diagram of an image frame produced at theprojection target by the image beam of the embodiment of FIG. 7.Referring to FIG. 7 and FIG. 9, in the embodiment, the image frameformed at the projection target P is produced by the image beams MLreflected by each of the second light splitting elements, i.e. the imageframe of a horizontal direction (the second direction X) viewed by humaneye.

Therefore, the image frame produced at the projection target P by theimage beams ML reflected by the different second light splittingelements is partially overlapped or connected, and if the image framehas a gap therein, the image viewed by the human eye has a black area.Therefore, as shown in FIG. 9, for example, different blocks of theimage frame produced at the projection target P are contributed by theimage beams ML reflected by different second light splitting elements,and image overlapping or image connection are occurred at a part of theblocks. Based on the design method of the diffusion coating film of theembodiment, the reflectivity of the N^(th) second light splittingelement in the second light splitting elements is smaller than or equalto the reflectivity of the (N+1)^(th) second light splitting element inthe second light splitting elements, and even if a part of the blocks isoverlapped, the image frame at the projection target P is stillmaintained uniform and has good display quality.

FIG. 10 is a side view of the first waveguide element of FIG. 1.Referring to FIG. 10, in the embodiment, each of the first lightsplitting elements Y1, Y2, Y3, Y4 includes a first surface and a secondsurface opposite to the first surface, where the first surface includesa diffusion coating film. One of the first surface and the secondsurface may include the diffusion coating film, and taking the firstlight splitting element Y1 as an example, the second surface SY22 isopposite to the first surface SY21, and the first surface SY21 includesthe diffusion coating film. In the embodiment and referring to FIG. 3,the optical axis A1 of the lens module 140 is parallel to the firstdirection Y and perpendicular to the visual axis A2 of the projectiontarget P, and the image beam ML is incident to the first surface SY21 ofthe first light splitting element Y1, and an incident angle thereof isbetween 30-60 degrees, where an included angle between each of the firstlight splitting elements of the first waveguide element 110 and thefirst light exiting surface S12 is 45 degrees, which may be 30 degreesin case of other design, though the invention is not limited thereto.Moreover, the reflectivity of an M^(th) first light splitting element issmaller than or equal to the reflectivity of an (M+1)^(th) first lightsplitting element, where M is an integer greater than or equal to 1. Forexample, the reflectivity of the 2^(nd) first light splitting element Y2is smaller than or equal to the reflectivity of the 3^(rd) first lightsplitting element Y3, such that a part of the image beam ML is reflectedto the second waveguide element 120 through the diffusion coating film,and the image frame formed at the projection target P is stillmaintained uniform and has good display quality. In another embodiment,referring to FIG. 2A, the optical axis A1 of the lens module 140 isperpendicular to the first direction Y and parallel to the visual axisA2 of the projection target P, the image beam ML is incident to thefirst surface SY21 of the first light splitting element, and 1 minus thereflectivity of the 1^(st) first light splitting element is smaller thanor equal to the reflectivity of the (M+1)^(th) first light splittingelement, where M is an integer greater than or equal to 1. For example,1 minus the reflectivity of the 1^(st) first light splitting element Y1is smaller than or equal to the reflectivity of the 2^(nd) first lightsplitting element. In this way, a part of the image beam ML is reflectedto the second waveguide element 120 by the diffusion coating film, andthe image frame formed at the projection target P is still maintaineduniform and has good display quality.

FIG. 11 is a schematic diagram of an image frame produced at theprojection target by the image beam of the embodiment of FIG. 10.Referring to FIG. 10 and FIG. 11, in the embodiment, the image frameformed at the projection target P is produced by the image beams MLreflected by each of the first light splitting elements. In other words,the image frame of a vertical direction (the first direction Y) viewedby human eye. Therefore, the image frame produced at the projectiontarget P by the image beams ML reflected by the different first lightsplitting elements is partially overlapped or connected, i.e. the imagebeams ML reflected by the different second light splitting elementsproduce an image frame on the projection target P, where the image frameis formed by the partially overlapped image beams ML, or the image beamsML reflected by the different second light splitting elements produce animage frame on the projection target P, where the image frame is formedby the partially connected image beams ML.

In other embodiments, the image beams ML reflected by the differentfirst light splitting elements and the image beams ML reflected by thedifferent second light splitting elements produce an image frame on theprojection target P, and the image frame is formed by the partiallyoverlapped image beams ML. In another embodiment, the image beams MLreflected by the different first light splitting elements and the imagebeams ML reflected by the different second light splitting elementsproduce an image frame on the projection target P, and the image frameis formed by the partially connected image beams ML. If the image framehas a gap therein, the image viewed by the human eye has a black area.Therefore, as shown in FIG. 11, different blocks of the image frameproduced at the projection target P are contributed by the image beamsML reflected by different first light splitting elements, and imageoverlapping or image connection are occurred at a part of the blocks,such that the image frame at the projection target P is still maintaineduniform and has good display quality.

FIG. 12A is a schematic diagram of superposing image frames produced atthe projection target by the image beam of the embodiments of FIG. 9 andFIG. 11. Referring to FIG. 9, FIG. 11 and FIG. 12A, the image beams MLrespectively reflected by each of the second light splitting elementsform the image frame of the horizontal direction (the second directionX) at the projection target P, and the image beams ML respectivelyreflected by each of the first light splitting elements form the imageframe of the vertical direction (the first direction Y) at theprojection target P, and the two image frames are superposed to form theimage frame at the projection target P.

FIG. 12B is a schematic diagram of reflecting the image beams to theprojection target by different second light splitting elements.Referring to FIG. 12, it is known that the image beams emit out of thesecond waveguide element in a diffusion manner through the second lightsplitting elements, though the position of the projection target P mayreceive the image beams projected by the second light splittingelements, and the projection target P may receive the partial overlappedimage beams or partial adjacent image beams to acquire a clear andintegral image.

FIG. 13 is a schematic diagram of the image beam incident to the secondwaveguide element from the first light splitting elements according toan embodiment of the invention. In FIG. 13, the image beam ML reflectedby the different first light splitting elements probably has differentincident angles when entering the second waveguide element 120 from thefirst waveguide element 110. Therefore, regarding the different firstlight splitting elements, the diffusion coating films thereof may beseparately designed. A chief ray of a part of the image beam reflectedby the first piece of the first light splitting elements (the firstlight splitting element Y1) is biased to the last piece of the firstlight splitting elements (the first light splitting element Y4). A chiefray of a part of the image beam reflected by the last piece of the firstlight splitting elements (the first light splitting element Y4) isbiased to the first piece of the first light splitting elements (thefirst light splitting element Y1). A direction of the image beam in FIG.13 is schematic, and the image beam is actually incident to the secondwaveguide element 120. For example, in FIG. 13, an angle between atransmitting direction (the first direction Y) of the image beam ML andthe first light splitting element is the incident angle, which is, forexample, 45 degrees, and the incident angle of the image beam MLincident to the first light splitting element is probably greater than,smaller than or equal to 45 degrees (a reference angle). For example,the incident angle of the image beam ML incident to the first lightsplitting elements Y1, Y2 is probably greater than 45 degrees. Referringto FIG. 14A, FIG. 14A is a schematic diagram of the image beam MLincident to the first light splitting element Y1, where an incidentangle thereof is greater than 45 degrees. The incident angle of theimage beam ML incident to the first light splitting element Y2 may bededuce by analogy. Therefore, regarding the design of the diffusioncoating film of the first light splitting elements Y1, Y2, at a placewhere the incident angle is greater than 45 degrees, the first lightsplitting elements Y1, Y2 have reflectivity of 15% and 30% at the regionwith the incident angle of 47 degrees and 50 degrees, such that theimage beam ML reflected to the second waveguide element 120 from thefirst light splitting elements Y1, Y2 have a larger light flux, and theefficiency of projecting the image beam ML to the projection target P isimproved. For another embodiment, the incident angle of the image beamML incident to the first light splitting elements Y3, Y4 is probablysmaller than 45 degrees, as shown in FIG. 14B. FIG. 14B is a schematicdiagram of the image beam ML incident to the first light splittingelement Y4, where an incident angle thereof is smaller than 45 degrees.The incident angle of the image beam ML incident to the first lightsplitting element Y3 may be deduce by analogy. Therefore, regarding thedesign of the diffusion coating film of the first light splittingelements Y3, Y4, at a place where the incident angle is smaller than 45degrees, the first light splitting elements Y3, Y4 have reflectivity of40% and 55% at the region with the incident angle of 40 degrees and 43degrees, such that the image beam ML reflected to the second waveguideelement 120 from the first light splitting elements Y3, Y4 have a largerlight flux, and the efficiency of projecting the image beam ML to theprojection target P is improved.

Therefore, in the embodiment of the invention, by adjusting an opticalcharacteristic of the diffusion coating film on the light splittingelements, the image frame on the projection target P is uniform, and theimage beam ML projected to the projection target P has larger lightflux.

A plurality of embodiments is provided below to describe an operationmethod of a HMD device including an illumination system, a displaydevice and a waveguide system.

FIG. 15 is a schematic diagram of a HMD device according to anembodiment of the invention. Referring to FIG. 15, the HMD device 300Aof the embodiment includes an illumination system 350A, a display device330A, a lens module 340 and a waveguide system. The lens module 340 mayinclude one or a plurality of lenses, and the waveguide system includesa first waveguide element 310 and a second waveguide element 320. In theembodiment, the display device 330A, for example, includes a digitallight processing™ (DLP™) projection system, which is used for convertingan illumination beam IL coming from the illumination system 350A intothe image beam ML. The image beam ML is transmitted to the projectiontarget P through the waveguide system. In the embodiment, enoughinstructions and recommendations for the operation method of thewaveguide system may be learned from the descriptions of the embodimentsof FIG. 1 to FIG. 14B.

In the embodiment, the illumination system 350A is used for providingthe illumination beam IL to the display device 330A. The illuminationsystem 350A includes an illumination light source 351, a collimationlens set 353, an aperture stop 355, a light uniforming element 357, anda prism module 359A. The illumination light source 351 provides theillumination beam IL. The illumination beam IL is transmitted to thedisplay device 330A through the collimation lens set 353, the aperturestop 355, the light uniforming element 357 and the prism module 359A. Inthe embodiment, the aperture stop 355 is disposed between thecollimation lens set 353 and the light uniforming element 357, and theillumination light source 351 is, for example, a light emitting diode(LED), though the invention is not limited thereto. The light uniformingelement 357 is, for example, a lens array. The lens array may be afly-eye lens array, and the collimation lens set 353 includes one or aplurality of lenses. In the embodiment, the illumination beam IL comingfrom the illumination light source 351 is converged to a third stop PA3in the illumination system 350A. The third stop PA3 is located at theaperture stop 355. In the embodiment, the aperture stop 355 may have adriving element 358 (for example, a motor), and the driving element isused for controlling an aperture size of the aperture stop 355, so as tocontrol an area of the third stop PA3. Therefore, the aperture stop 355may adjust a light flux of the illumination beam IL passingtherethrough. In the embodiment, the prism module 359A includes a prism352 (a first prism). The illumination beam IL coming from the lightuniforming element 357 is transmitted to the display device 330A throughthe prism 352. In another embodiment, according to a design requirement,the aperture of the aperture stop 355 may have a fixed aperture size.

FIG. 16 is a schematic diagram of a HMD device according to anembodiment of the invention. Referring to FIG. 15 and FIG. 16, the HMDdevice 300B of the embodiment is similar to the HMD device 300A of FIG.15, and a main difference therebetween, for example, lies in designs ofthe illumination system 350B and the display device 330B.

To be specific, in the embodiment, the display device 330A, for example,includes a liquid crystal on silicon (LCoS) projection system, which isused for converting the illumination beam IL coming from theillumination system 350B into the image beam ML. The image beam ML istransmitted to the projection target P through the waveguide system. Inthe embodiment, enough instructions and recommendations for theoperation method of the waveguide system may be learned from thedescriptions of the embodiments of FIG. 1 to FIG. 14B. In theembodiment, the illumination system 350B is used for providing theillumination beam IL to the display device 330B. The aperture stop 355is disposed between the collimation lens set 353 and the lightuniforming element 357. In the embodiment, the illumination beam ILcoming from the illumination light source 351 is converged to the thirdstop PA3 in the illumination system 350A. The illumination beam IL ofthe illumination light source 351 may be converted into the illuminationbeam IL with a single polarity though polarity conversion. The thirdstop PA3 is located at the aperture stop 355. In the embodiment, theaperture stop 355 may have a driving element. The driving element isused for controlling an aperture size of the aperture stop 355, so as tocontrol an area of the third stop PA3. Therefore, the aperture stop 355may adjust a light flux of the illumination beam IL passingtherethrough. In the embodiment, the prism module 359B includes apolarizing beam splitter (PBS). The illumination beam IL coming from thelight uniforming element 357 is transmitted to the display device 330Athrough the PBS, and is reflected to the lens module 340.

FIG. 17 is a schematic diagram of a HMD device according to anembodiment of the invention. Referring to FIG. 15 and FIG. 17, the HMDdevice 300C of the embodiment is similar to the HMD device 300A of FIG.15, and a main difference therebetween, for example, lies in a design ofthe prism module 359C.

To be specific, in the embodiment, the display device 330C, for example,includes a digital light processing™ (DLP™) projection system, which isused for converting an illumination beam IL coming from the illuminationsystem 350C into the image beam ML. The image beam ML is transmitted tothe projection target P through the waveguide system. In the embodiment,enough instructions and recommendations for the operation method of thewaveguide system may be learned from the descriptions of the embodimentsof FIG. 1 to FIG. 14B. In the embodiment, the prism module 359C includesa first prism 359_1, a second prism 359_2 and a third prism 359_3. Thefirst prism 359_1 has a curved surface, and the curved surface has areflection layer R. The curved surface is used for reflecting theillumination beam IL coming from the light uniforming element 357. Inthe embodiment, a tiny air gap is formed between every two prisms. Forexample, a first gap is located between the first prism 359_1 and thesecond prism 359_2, and a second gap is located between the second prism359_2 and the third prism 359_3. The illumination beam IL coming fromthe light uniforming element 357 is transmitted to the display device330C through the first prism 359_1, the first gap, the curved surface,the second prism 359_2, the second gap and the third prism 359_3. In anembodiment, the first prism 359_1 may be attached to the second prism359_2, or the first prism 359_1 and the second prism 359_2 may beadhered through a transparent adhesive. The second prism 359_2 may beattached to the third prism 359_3, or the second prism 359_2 and thethird prism 359_3 may be adhered through the transparent adhesive.

In the embodiment of FIG. 15 to FIG. 17, the illumination systems 350A,350B, 350C have a first F value, and the first F value is determinedaccording to an area size of the third stop PA3. The lens module 340 hasa second F value. The HMD devices 300A, 300B, 300C are complied with acondition that the first F value is greater than or equal to the secondF value, which mitigate a ghost phenomenon of the image frame. The Fvalue may be defined as ½*sin(θ), where the angle θ is a cone angle forlight incidence.

For example, FIG. 18 is a schematic diagram of a part of elements of theHMD device of the embodiment of FIG. 17. For simplicity's sake, only thedisplay device 330C, the third prism 359_3 and the lens module 340 ofthe HMD device 300C are illustrated in FIG. 18. In the embodiment, theillumination beam IL is incident to the display device 330C, where thedisplay device 330C, for example, includes a digital micromirror device(DMD). The DMD first converts the illumination beam IL into the imagebeam ML, and reflects the image beam ML to the third prism 359_3. Thethird prism 359_3 then reflects the image beam ML to the lens module340. In the embodiment, the cone angle of the illumination beam ILincident to the display device 330C is, for example, θ1, and the first Fvalue of the illumination system 350C may be defined as ½*sin(θ1). Inthe embodiment, the lens module 340 receives the image beam ML comingfrom the display device 330C, where the cone angle thereof is, forexample, θ2. The second F value of the lens module 340 may be defined as½*sin(θ2).

In the embodiment, according to manufacturer's design, the second Fvalue of the lens module 340 is preset, i.e. the required incident angleθ2 is learned, so that the aperture size of the aperture stop 355 may beadjusted to control a size of the third stop PA3, and the size of thethird stop PA3 influences a magnitude of the cone angle θ1 of theillumination beam IL incident to the display device 330C. Namely, afterthe second F value of the lens module 340 is determined, a magnitude ofthe first F value of the illumination system 350C may be controlledthrough the aperture stop 355, such that the HMD device 300C may becomplied with the condition that the first F value is greater than orequal to the second F value. In an embodiment, the aperture of theaperture stop 355 may have a fixed aperture size, and through a designof the second F value of the lens module 340, the first F value of theillumination system 350C is designed to make the HMD device 300C to becomplied with the condition that the first F value is greater than orequal to the second F value. In the embodiments of FIG. 15 and FIG. 16,the illumination systems 350A, 350B may also be adjusted according tothe above method, such that the HMD devices 300A, 300B are complied withthe condition that the first F value is greater than or equal to thesecond F value. Therefore, during the process that the user uses the HMDdevices 300A, 300B, the ghost phenomenon of the image frame is mitigatedor a phenomenon that the image frame becomes blurred is avoided.

FIG. 19 is a schematic diagram of a HMD device according to anembodiment of the invention. Referring to FIG. 15 and FIG. 19, the HMDdevice 400A of the embodiment is similar to the HMD device 300A of FIG.15, and a main difference therebetween is that a configuration positionof an aperture stop 455 is different and a light uniforming element 457is a light integration rod.

To be specific, in the embodiment, a prism module 459A includes a prismand two lenses, where the aperture stop 455 is disposed between the twolenses, and the light uniforming element 457 is, for example, a lightintegration rod. In the embodiment, the illumination beam IL coming froman illumination light source 451 is converged to the third stop PA3 inthe illumination system 450A. The third stop PA3 is located at theaperture stop 455. In the embodiment, the aperture stop 455 may have adriving element. The driving element is used for controlling an aperturesize of the aperture stop 455, so as to control a size of the third stopPA3, and control a magnitude of the cone angle of the illumination beamIL incident to the display device 430A. Therefore, after the second Fvalue of the lens module 440 is determined, a magnitude of the first Fvalue of the illumination system 450A may be controlled through theaperture stop 455, such that the HMD device 400A may be complied withthe condition that the first F value is greater than or equal to thesecond F value.

FIG. 20 is a schematic diagram of a HMD device according to anembodiment of the invention. Referring to FIG. 16 and FIG. 20, the HMDdevice 400B of the embodiment is similar to the HMD device 300B of FIG.16, and a main difference therebetween is that a configuration positionof the aperture stop 455 is different and the light uniforming element457 is a light integration rod.

To be specific, in the embodiment, a prism module 459B includes twoprisms and two lenses, where the aperture stop 455 is disposed betweenthe two lenses of the prism module 459B, and the light uniformingelement 457 is, for example, a light integration rod. In the embodiment,the illumination beam IL coming from the illumination light source 451is converged to the third stop PA3 in the illumination system 450A. Thethird stop PA3 is located at the aperture stop 455. In the embodiment,the aperture stop 455 may have a driving element. The driving element isused for controlling an aperture size of the aperture stop 455, so as tocontrol a size of the third stop PA3, and control a magnitude of thecone angle of the illumination beam IL incident to the display device430A. Therefore, after the second F value of the lens module 440 isdetermined, a magnitude of the first F value of the illumination system450A may be controlled through the aperture stop 455, such that the HMDdevice 400A may be complied with the condition that the first F value isgreater than or equal to the second F value.

FIG. 21 is a schematic diagram of a HMD device according to anembodiment of the invention. Referring to FIG. 21, the HMD device 400Cof the embodiment includes an illumination system 450C, a display device430C, a lens module 440 and a waveguide system. The waveguide systemincludes a first waveguide element 410 and a second waveguide element420. In the embodiment, the display device 430C, for example, includes adigital light processing™ (DLP™) projection system or a LCoS projectionsystem, which is used for converting an illumination beam IL coming fromthe illumination system 450C into the image beam ML. The image beam MLis transmitted to the projection target P through the waveguide system.In the embodiment, enough instructions and recommendations for theoperation method of the waveguide system may be learned from thedescriptions of the embodiments of FIG. 1 to FIG. 14B.

In the embodiment, the illumination system 450C is used for providingthe illumination beam IL to the display device 430C. The illuminationsystem 450C includes the illumination light source 451, the lightuniforming element 457, a collimation lens set 453C, the aperture stop455, and a prism module 459C. The illumination light source 451 providesthe illumination beam IL. The illumination beam IL is transmitted to thedisplay device 430C through the light uniforming element 457, theaperture stop 455, the collimation lens set 453C and the prism module459C. In the embodiment, the collimation lens set 453C includes lenses4531 and 4532. The aperture stop 455 is disposed between the lenses453_1 and 453_2 of the collimation lens set 453C. The light uniformingelement 457 is, for example, a light integration rod. In the embodiment,the illumination beam IL coming from the illumination light source 451is converged to the third stop PA3 in the illumination system 450C. Thethird stop PA3 is located at the aperture stop 455. In the embodiment,the aperture stop 455 may have a driving element, and the drivingelement is used for controlling an aperture size of the aperture stop455, so as to control a size of the third stop PA3. Therefore, theaperture stop 455 may adjust a light flux of the illumination beam ILpassing therethrough. In the embodiment, the prism module 459C includesa first prism 352_1 and a second prism 352_2. The illumination beam

IL coming from the collimation lens set 453C is transmitted to thedisplay device 430C through the reflection of the first prism 352_1, andthe illumination beam IL is converted into the image beam ML andtransmitted to the lens module 440 through the second lens 352_2.

In the embodiment, the aperture size of the aperture stop 455 may beadjusted to control a size of the third stop PA3, and the size of thethird stop PA3 may influence a magnitude of the cone angle θ1 of theillumination beam IL incident to the display device 430C. Therefore,after the second F value of the lens module 440 is determined, amagnitude of the first F value of the illumination system 450C may becontrolled through the aperture stop 455, such that the HMD device 400Cmay be complied with the condition that the first F value is greaterthan or equal to the second F value.

In summary, in the exemplary embodiments of the invention, the firststop is located within the first waveguide element, the second stop islocated at the projection target, such that the HMD device may provide alarge FOV, and a volume of the waveguide system is decreased. In theexemplary embodiments of the invention, the diffusion coating film ofeach of the light splitting elements may be determined according todifferent reflectivity requirements or product designs, so that theimage frame at the projection target is maintained uniform and has goodimage quality. In the exemplary embodiments of the invention, the thirdstop is located in the illumination system, and the aperture stop isdisposed at the third stop. The HMD device may the third stop and amagnitude of the first F value of the control system by adjusting theaperture stop, such that the HMD device is complied with the conditionthat the first F value is greater than or equal to the second F value,so as to mitigate the ghost phenomenon of the image frame to providegood image quality.

The foregoing description of the preferred embodiments of the inventionhas been presented for purposes of illustration and description. It isnot intended to be exhaustive or to limit the invention to the preciseform or to exemplary embodiments disclosed. Accordingly, the foregoingdescription should be regarded as illustrative rather than restrictive.Obviously, many modifications and variations will be apparent topractitioners skilled in this art. The embodiments are chosen anddescribed in order to best explain the principles of the invention andits best mode practical application, thereby to enable persons skilledin the art to understand the invention for various embodiments and withvarious modifications as are suited to the particular use orimplementation contemplated. It is intended that the scope of theinvention be defined by the claims appended hereto and their equivalentsin which all terms are meant in their broadest reasonable sense unlessotherwise indicated. Therefore, the term “the invention”, “the presentinvention” or the like does not necessarily limit the claim scope to aspecific embodiment, and the reference to particularly preferredexemplary embodiments of the invention does not imply a limitation onthe invention, and no such limitation is to be inferred. The inventionis limited only by the spirit and scope of the appended claims.Moreover, these claims may refer to use “first”, “second”, etc.following with noun or element. Such terms should be understood as anomenclature and should not be construed as giving the limitation on thenumber of the elements modified by such nomenclature unless specificnumber has been given. The abstract of the disclosure is provided tocomply with the rules requiring an abstract, which will allow a searcherto quickly ascertain the subject matter of the technical disclosure ofany patent issued from this disclosure. It is submitted with theunderstanding that it will not be used to interpret or limit the scopeor meaning of the claims. Any advantages and benefits described may notapply to all embodiments of the invention. It should be appreciated thatvariations may be made in the embodiments described by persons skilledin the art without departing from the scope of the invention as definedby the following claims. Moreover, no element and component in thedisclosure is intended to be dedicated to the public regardless ofwhether the element or component is explicitly recited in the followingclaims.

What is claimed is:
 1. A head-mounted display device, comprising: adisplay device, configured to provide an image beam, wherein the imagebeam is projected to a projection target; a first waveguide element,comprising: a first light incident surface; a first light exitingsurface; and a plurality of first light splitting elements, wherein theimage beam coming from the display device is incident to the firstwaveguide element through the first light incident surface, the imagebeam is convergent to a first stop, and the image beam leaves the firstwaveguide element through the first light exiting surface, wherein thefirst stop is located in the first waveguide element; and a secondwaveguide element, comprising: a second light incident surface; a secondlight exiting surface; and a plurality of second light splittingelements, wherein the image beam coming from the first waveguide elementis incident to the second waveguide element through the second lightincident surface, and the image beam leaves the second waveguide elementthrough the second light exiting surface.
 2. The head-mounted displaydevice of claim 1, wherein the image beam leaves the second waveguideelement through the second light exiting surface, and the image beam isprojected to a second stop outside the second waveguide element, whereinthe second stop is located at the projection target.
 3. The head-mounteddisplay device of claim 1, wherein the first light splitting elementsare arranged along a first direction, a distance between the first stopand a center position of a first piece of the first light splittingelements in the first direction is D1, and a distance between areference axis and the center position of the first piece of the firstlight splitting elements in the first direction is D2, wherein thedistance D1 is greater than or equal to the distance D2, and theprojection target has a visual axis perpendicular to the firstdirection, the visual axis is translated to the reference axis on areference plane in the first waveguide element, and the reference planepasses through the center position of the first piece of the first lightsplitting elements.
 4. The head-mounted display device of claim 3,wherein the second light splitting elements are arranged along thesecond direction, the image beam is transmitted along the firstdirection in the first waveguide element, and the image beam isreflected by the first light splitting elements to leave the firstwaveguide element.
 5. The head-mounted display device of claim 4,further comprising: a lens module, having an optical axis, and the lensmodule being disposed between the display device and the first waveguideelement, wherein the lens module is configured to produce a field ofview corresponding to a field of view of the image beam received at theprojection target.
 6. The head-mounted display device of claim 5,wherein the optical axis of the lens module is perpendicular to thefirst direction and parallel to the visual axis of the projectiontarget, and a diagonal field of view of an image formed by the imagebeam received at the projection target is 30-50 degrees.
 7. Thehead-mounted display device of claim 5, wherein the optical axis of thelens module is parallel to the first direction and perpendicular to thevisual axis of the projection target, and a diagonal field of view of animage formed by the image beam received at the projection target is50-90 degrees.
 8. The head-mounted display device of claim 5, wherein adiagonal field of view of an image formed by the image beam received atthe projection target is 30-90 degrees.
 9. The head-mounted displaydevice of claim 5, wherein the field of view produced by the lens modulecomprises a first field of view and a second field of view, a magnitudeof the first field of view is determined according to the firstwaveguide element, and a magnitude of the second field of view isdetermined according to the second waveguide element.
 10. Thehead-mounted display device of claim 1, wherein the first light incidentsurface is disposed opposite to the first light exiting surface, and theoptical axis of the lens module is perpendicular to the first direction.11. The head-mounted display device of claim 1, wherein the first lightincident surface is connected to the first light exiting surface, andthe optical axis of the lens module is parallel to the first direction.12. The head-mounted display device of claim 1, wherein the first lightincident surface is connected to the first light exiting surface, andthe optical axis of the lens module is perpendicular to the firstdirection and parallel to the second direction.
 13. The head-mounteddisplay device of claim 1, wherein the second light incident surface andthe second light exiting surface are the same surface.
 14. Thehead-mounted display device of claim 1, wherein the first waveguideelement and the second waveguide element have a gap therebetween. 15.The head-mounted display device of claim 1, wherein the a quantity ofthe second light splitting elements of the second waveguide element isgreater than a quantity of the first light splitting elements of thefirst waveguide element.
 16. A head-mounted display device, comprising:a first waveguide element, comprising: a first light incident surface; afirst light exiting surface; and a plurality of first light splittingelements, wherein an image beam is incident to the first waveguideelement through the first light incident surface, the image beam isconvergent to a first stop in the first waveguide element, and the imagebeam leaves the first waveguide element through the first light exitingsurface, wherein the first stop is located in the first waveguideelement; and a second waveguide element, comprising: a second lightincident surface; a second light exiting surface; and a plurality ofsecond light splitting elements, wherein the image beam coming from thefirst waveguide element is incident to the second waveguide elementthrough the second light incident surface, and the image beam leaves thesecond waveguide element through the second light exiting surface. 17.The head-mounted display device of claim 16, wherein the image beamleaves the second waveguide element through the second light exitingsurface, and the image beam is projected to a second stop outside thesecond waveguide element, wherein the second stop is located at theprojection target.
 18. The head-mounted display device of claim 16,wherein the image beam is provided by a display device and the imagebeam is projected to the projection target.